The present invention relates to an image processing device that processes a signal output from an image sensor and outputs the processed signal.
In digital cameras that use a charge-coupled device (CCD), a complementary metal oxide semiconductor (CMOS) image pickup device or the like as the image sensor, such as digital still cameras, digital camera-equipped mobile phones and digital video cameras, an image processing device performs image processing for an image signal read from the image sensor and outputs the results to a display device. In this relation, reading of an image from the image sensor and outputting of the image signal to the display device are made every line of a frame. Accordingly, in many cases, each function block of the image processing device performs its processing using a line memory that can store data by line.
With the increase of the number of pixels of image sensors, the number of pixels of one line has increased and this has raised the need for increasing the capacity of line memories. To respond to this need, there is disclosed an image processing device in which an external memory capable of storing data of one entire frame is used and image processing is performed by block (see Japanese Laid-Open Patent Publication No. 2000-354193, for example).
FIG. 16 is a block diagram of an example of a conventional camera, showing a configuration disclosed in the publication described above. In FIG. 16, an image signal read from an image sensor by line is stored in an external memory 914. An image processing device (signal processing circuit) 916 performs image processing for the image signal stored in the external memory 914 by reading the image signal by block, and stores the processed signal again in the external memory 914. A display device reads the processed signal from the external memory 914 for display.
Recent digital cameras are requested to achieve various extended functions of scaling down an image, rotating an image and the like, in addition to the function of taking pictures. They are also requested to provide a plurality of image-quality modes in consideration of the capacities of recording media. In other words, the image processing device is required to perform a plurality of processing items, and the capacity of the memory required and the way of use of the memory vary with the processing item.
In the camera of FIG. 16, image processing is performed by block. Accordingly, four times of access to the external memory 914 are necessary whichever type of processing is to be performed. Specifically, access to the external memory is necessary when an image signal read from the image sensor by line is written, when the image processing device reads the stored image signal by block, when the image-processed data is written by block, and when the stored image-processed signal is read for display.
In general, access to an external memory consumes much power and requires long processing time, compared with access to an internal memory. Accordingly, a system as that described above that makes access to an external memory invariably during image processing has a problem that at least some amounts of power and processing time are necessary regardless of the type of the processing.
In the processing by block, data of a pixel belonging to a plurality of blocks in duplication is read a plurality of times. Therefore, the number of times of access to the external memory increased compared with the case of reading data once for each pixel. This also causes a problem in power consumption and processing time.
Image processing devices can be mounted in various systems such as digital still cameras, digital video cameras and digital camera-equipped mobile phones. The functions required for the image processing devices however differ among the systems. For example, in digital still cameras, in which an image having a large number of pixels must be processed, extended functions such as on-screen display (OSD) processing and rotation are naturally required. In digital camera-equipped mobile phones, in which the number of pixels of an image processed is small, extended functions such as scaledown and rotation are not required in many cases. In this case, therefore, no external memory is necessary. However, in the prior art disclosed in the above publication, the image processing device inevitably requires the external memory regardless of the system for which the image processing device is used.
Different image processing devices may be mounted in different systems. Recently, however, reduction in the development cost of image processing devices has been strongly requested. In this situation, it is desired that one type of image processing device can be used for a plurality of systems.